Under the Volcano
(1984)

The Consul Geoffrey Firmin (Albert Finney) wanders away from his estranged wife Yvonne (Jacqueline Bisset) and his brother Hugh (Anthony Andrews), and heads down a forest trail in search of a place to get drunk. He finds a bar he has not set foot in for a long time, and the bartender gives him a stack of unread, unopened letters Yvonne had sent to him there.

Geoffrey gets into a quarrel with some corrupt local police, who take him outside, shoot him, and dump his body into a ditch. In the process, the police startle a horse, who runs down the forest path in a panic, accidentally trampling Yvonne to death.

Thanks John L!